A leaky wave antenna that uses a composite right/left-handed transmission line has been proposed as one of applications that use “metamaterials” formed of periodic structures sufficiently smaller than wavelengths of electromagnetic waves. The composite right/left-handed transmission line can be obtained by introducing capacitance components into a series part of a normal host line having a right-handed characteristic and introducing inductance components into a shunt part of the same host line.
For example, in a structure disclosed in the specification of U.S. Pat. No. 7,592,957 (Patent Literature 1), titled “ANNTENNAS BASED ON METAMATERIAL STRUCTURES”, a capacitance between “Cell Conductive Patches” (conductive patches) and an inductance by a “Cell Conductive Via” (conductive via) are introduced into a microstrip line, which is a host line, whereby a Composite Right/Left-Handed (CRLH) transmission line is obtained.
In the composite right/left-handed transmission line, in a frequency band in which the phase of electromagnetic waves propagating through the transmission line matches the phase of electromagnetic waves that may exist in a free space, the electromagnetic waves propagating through the transmission line leak out to the free space. The antenna thus serves as the leaky wave antenna. The leaky wave antenna is able to efficiently radiate radio waves in a frequency region wider than that of normal resonant antennas. Further, the leaky wave antenna that uses the composite right/left-handed transmission line is able to radiate radio waves in broad angles from forward to backward with respect to the power propagation direction depending on the frequency.